Changes/RPMSuportForSystemdSysusers

RPM Support For Systemd Sysusers.d

Summary

RPM supports creating users and groups according to configuration provided in sysusers.d snippets shipped in package payload.

The goal of the proposal is to fully integrate this RPM functionality in Fedora.

Owner

• Name: Michal Sekletar, Zbigniew Jędrzejewski-Szmek, Panu Matilainen
• Email: msekleta@redhat.com, zbyszek@in.waw.pl, pmatilai@redhat.com

Current status

• Targeted release: Fedora Linux 42
• Last updated: 2025-01-10
• Announced
• Discussion thread
• FESCo issue: #3318
• Tracker bug: #2337007
• Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

This proposal consists of two parts. The first is to make sure that rpm functionality is fully enabled in Fedora. The second is to update packaging guidelines and raise awareness about the new simpler user creation method for rpm packages. The goal is a fully declarative system user and group management in all RPMs. Over time we should be able to drop all manual useradd/groupadd invocations or use of %sysusers_create_compat macro in rpm scriptlets.

Support for sysusers was added in rpm 4.19.0. Support for group membership (m lines) was added in rpm 4.20.0. Support for locked-down users (u! lines) was added for next rpm version (release number TBD). The rpm package has patches to disable user/group creation (rpm-4.18.92-disable-sysusers.patch) and make user/group dependencies weak (rpm-4.19.91-weak-user-group.patch).

Some useful introspection commands:

• sysusers metadata on installed packages:
  rpm -q --qf "[%{SYSUSERS}\n]" -a
• sysusers config known to systemd:
  systemd-sysusers --cat-config
  or
  systemd-sysusers --tldr
• all sysusers definitions on packages in repos:
  dnf repoquery --provides | rg '^(user|group)\('

Feedback

Discussion about idea to submit the proposal on fedora-devel list.

Benefit to Fedora

• Declarative system user and group management by packages
• Potential for spec file simplification, concretely, removal of relevant part of %pre scripts in some packages.
• Ability to query what user and groups are provided by given package as well as ability to have dependencies on users/groups from different packages.
• Make use of native rpm functionality in favor of current %sysusers_compat_create.

Scope

• Proposal owners:
  • Change rpm so that it generates hard dependency between packages A and B in case B depends on user or group provided by package A. Rpm currently has downstream patch so that only weak dependencies are generated.
  • Make sure that previous change in rpm doesn't cause package dependency loops during system installation.
  • Work on fix for shadow-utils so that useradd and groupadd work correctly in chroot on SELinux enabled systems (shadow-utils issue.)
• Other developers:
  • We would welcome any help with shadow-utils issue.

• Release engineering: N/A (not needed for this Change)

• Policies and guidelines: N/A (not needed for this Change)

• Trademark approval: N/A (not needed for this Change)

• Alignment with the Fedora Strategy:

Upgrade/compatibility impact

There is no upgrade/compatibility impact.

How To Test

• Select rpm package that creates system user/group account in %pre
• Remove part of %pre scriptlet that handles user/group creation
• Create equivalent sysusers.d configuration file and ship it as part of rpm payload under /usr/lib/sysusers.d/.
• Rebuild the package
• Verify that package has been built correctly and it has rpm provides for installed user account and group (e.g. user(foo) = ABUNCHOFHEXHERE, group(bar) = ADIFFERNTBUNCHOFHEXHERE). Use rpm -q --qf "[%{SYSUSERS}\n]" $package and check that the output looks reasonable.
• Verify that you can install the package and installed files have correct ownership.
• Verify that audit events were logged for user and group creation:
  ausearch --start recent -i -m 'ADD_USER,USER_MGMT,USER_CHAUTHTOK,ROLE_ASSIGN,ROLE_REMOVE,DEL_USER,ADD_GROUP,GRP_MGMT,GRP_CHAUTHTOK,DEL_GROUP'

User Experience

There shouldn't be any user observable change to previous state. Potential packaging related benefits are mostly of interest to package maintainers.

Dependencies

None

Contingency Plan

• Contingency mechanism: If we are not confident by mass-rebuild that we can deliver the feature we will postpone its delivery to later Fedora release. There are no explicit rollback/cleanup actions that need to taken.
• Contingency deadline: Mass Rebuild of RPMs on Wed 2025-01-15.
• Blocks release? No

Documentation

sysusers.d support in RPM.

Release Notes

The built-in rpm mechanism to create system users from sysusers.d metadata distributed by packages is now used to create system users, replacing the previous use of custom rpm scriptlets in individual packages.